Reports and Proceedings — Oeological Society of London. 229 



1881 by Professor Bonney, and notices some important outcrops 

 near Llyn Dinam and Llyn Penrbyn. 



In tbe serpentine, enstatite frequentlj'^, and diallage sometimes, 

 are present; these crystals being occasionally lustre-mottled. Tbe 

 most remarkable variety (wbicb occurs distinctly at seven localities, 

 altbougb generally over a surface of only a few square feet) is tbat 

 termed 'variolitic serpentine.' On a weatbered surface knobs project 

 as upon a variolitic diabase; tbese, under tbe microscope, are found to 

 consist mainly of fibrous aggregates, probably actinolitic, sometimes 

 exbibiting a radial structure, but rarely a concentric one. A carbonate 

 is also present in variable amounts. Tbe authors think that probably 

 the original magma of this rock was differentiated, one part repre- 

 senting a pyroxenic constituent and becoming modified by alteration 

 into tbe spherules ; the other (olivine) producing ordinary serpentine. 



Intrusive in the serpentine are diallage-rock, enstatite-rock, and 

 rocks composed of both these minerals, all usually containing some 

 serpentine. Various actinolitic rocks, often truly ' actinolitic schists,' 

 probably have been derived through crushing from a diallage-rock 

 (or one allied to it). Other intrusive rocks are the gabbro, wbicb 

 forms large important masses, a dyke of enstatite-gabbro, a por- 

 pbyrite (?), and some greenstones. 



A secondary development of tufted actinolite (compared by tbe 

 authors with the actinolite in true schists, and with that in the 

 Bastogne rock) is described from at least four localities. It is 

 probably an indirect result of crushing in rocks which, though 

 petrograpbically different, all originally contained a pyroxenio 

 mineral which has been reconstituted. 



Further details are given of the talc-schist and the chlorite-schist in 

 this district, confirming the views that the former rock is a modifica- 

 tion of a serpentine, and that the latter was originally intrusive. 



Tbe age of these igneous rocks cannot be determined ; but they 

 must be earlier than the great earth-movements to which the 

 pressure-structures are due. 



'Z. " Remarks on the Genera Ectomaria, Kokeu, and Hormotoma, 

 Salter ; with Descriptions of the British Species." By Miss Jane 

 Donald. (Communicated by J. G. Goodcbild, Esq., F.G.S.) 



This paper deals with some of tbe genera into which the family 

 of the MurchisoniidEe has been divided, and confines itself to the 

 established genus Hormotoma, Salter, and tbe new genus Ectomaria, 

 Koken, which contain some of the oldest known species of elongated 

 Gasteropoda. Both forms are distinguished from the typical 

 MurcMsonicB by merely possessing a sinus in the outer lip, instead 

 of having a deep narrow slit with parallel edges ; the lines of 

 growth also retreat towards, and advance from, the sinus more 

 obliquely. The author prefers to separate the elongated shells from 

 the shorter Pleurotomariidee, as Koken does, and to let the former 

 constitute the family Murchisoniidee. 



The genera are described with two new species of Ectomaria and 

 two new varieties of Ectomaria pagoda, Salt. Six new species of 

 Hormotoma are also described, together with the species H. Salter i, 



